Ok...18 plates...810lbs I believe. Let's say that the sled somehow weighed 90lbs. So...you've got 900lbs on the leg press. WoW. Factor in the fact that with the angle of the leg press...you are probably only pushing about 300-400lbs. Ok...so you are doing reps with say 350 on the squat...and not even a full squat if you are trying to compare it to the leg press.
My point being...comparing the leg press and the squat is like comparing apples and oranges. They are both good, but you can't get apple juice from oranges.
I do not mean to put you down at all..by all means...18 plates is a good bit on the leg press for high reps. I am just trying to say that the leg press does not transer over into the squat. The squat is the king of the lower body and the erectors.
I've spent all weekend watching Louie Simmons tapes of West Side methods of training. Inspiring. Never did I see them do a leg press...just variations of the squat. He also said...over and over...do not train around your weak points. You will only be as strong as your weakest link. If you have a weak link, train it and train it hard. If your back hurts when you squat, then you have a weak back. Strengthen it. Fix the problem, do not make an excuse not to squat.
I will say this. If you have some sort of major spinal or bone structure problem...then all of this is out the window. Do what you can with what you have...trust me...I know.
In my humble opinion, it is better to squat without intensity than to leg press with intensity. You will still grow more from the squat if done properly..and you will strengthen your abs, erectors, back, glutes, hams, calves, etc.....
Sorry about the long post, and I hope that I did not offend anyone...that was not my intention. If I can help anyone on here...please let me know and feel free to email me anytime.
B True